1. Field of the Invention
The present invention relates to a dielectric filter and a dielectric duplexer, and more specifically, to a dielectric filter and a dielectric duplexer for dual bands be used in communication devices, etc., for the microwave band and the millimeter wave band.
2. Description of the Related Art
A dual-band high frequency circuit part to be used for a communication device for the microwave band or the millimeter wave band has been constituted by combining two band pass filters 101,121 shown in FIGS. 10 and 11. The band pass filter 101 shown in FIG. 10 is provided with three resonators utilizing a TEM mode.
In FIG. 10, the high frequency circuit part comprises a dielectric block 102, through holes 103 in which an inner conductor is provided on an inner wall surface, electrode patterns 104 for regulating the respective resonance frequency of TEM mode resonators and the electromagnetic coupling therewith, an outer conductor 105 provided on an outer surface of the dielectric block 102 except for an open end surface 102a, and input/output electrodes 106 for TEM mode.
The band pass filter 121 shown in FIG. 11 is provided with three resonators utilizing a TE mode. In FIG. 11, the band pass filter is provided with a dielectric block 122, a line conductor 123 for TE mode coupling, outer conductors 124a, 124b which are provided on upper and lower surfaces of the dielectric block 122 and electrically connected to each other via the line conductor 123, and input/output electrodes 125 for TE mode.
Apart from the above described structure, in some cases the dual band high frequency circuit part comprises a band pass filter of one-input/two-output type which provides a duplexer.
However, in either case, there is enough problem that a space to be occupied by two band pass filters is required when the above described filters are mounted on a printed circuit board, etc.
To solve this problem, composite parts miniaturized by integrating the TEM mode band pass filter 101 and the TE mode band pass filter 121 which are illustrated in FIGS. 10 and 11 respectively, can be designed. However, simply integrating the TEM mode band pass filter 101 and the TE mode band pass filter 121 requires the line conductor 123 for the TE mode coupling to be disposed between the electrode patterns 104 formed on the open end surface 102a of the TEM mode band pass filter 101, and the electromagnetic coupling of the TEM mode resonators with each other is affected by the line conductor 123. Thus, it is difficult to independently design the TEM mode band pass filter and the TE mode band pass filter. In addition, the electrode patterns 104 are provided on the open end surface 102a, and the position where the line conductor 123 is formed is limited to a specific part of the open end surface 102a, raising a new problem that the resonance frequency of the TE mode resonator and the setting of the number of the resonators are restricted.